1. Field of the Invention
The present invention relates to a merged MR head made by notching the first pole piece of the head""s write element and also to forming a notched first pole piece with a first pole piece layer and a notching layer and then milling a gap layer and the notching layer, employing a second pole tip as a mask, until side walls of the second pole tip, the gap layer and the notching layer are contiguous.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces have first and second pole tips, respectively, which terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces write fields in the first and second pole pieces. A nonmagnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS fringe across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to, and a short distance (fly height) from, the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR read head.
An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers, and located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head, the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic fields from the circular tracks of the rotating disk by a change in resistance that corresponds to the strength of the fields. A sense current is conducted through the MR sensor, where changes in resistance cause voltage changes that are received by the processing circuitry as readback signals.
One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged MR head is mounted on a slider that is carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates, an air layer (an xe2x80x9cair bearingxe2x80x9d) is generated between the rotating disk and an air bearing surface (ABS) of the slider. A force of the air bearing against the air bearing surface is opposed by an opposite loading force of the suspension, causing the magnetic head to be suspended a slight distance (flying height) from the surface of the disk. Flying heights are typically on the order of about 0.05 xcexcm
The second pole, along with its second pole tip, is frame-plated on top of the gap layer. After depositing a seed layer on the gap layer, a photoresist layer is spun on the seed layer, imaged with light, and developed to provide an opening surrounded by a resist wall for plating the second pole piece and second pole tip. To produce a second pole tip with a narrow track width, the photoresist layer has to be correspondingly thin. This relationship, referred to as the xe2x80x9caspect ratioxe2x80x9d, is the ratio of the thickness of the photoresist in the pole tip region to the track width of the second pole tip. Preferably, the aspect ratio should be on the order of three. In other words, for a track width of 1 xcexcm, the thickness of the photoresist in the pole tip region should be about 3 xcexcm. If the photoresist is thicker than this, the side walls of the second pole tip, especially at the base, will not be well-formed due to scattering of light as it penetrates the photoresist during the imaging step.
Once the second pole tip is formed, it is desirable to notch the first pole piece opposite the first and second bottom corners of the second pole tip. Notching the first pole piece minimizes side writing in tracks written on the magnetic disk. As is known, when the tracks are overwritten by side writing the track density of the magnetic disk is reduced. When the first pole piece is notched, it has first and second side walls that are aligned with first and second side walls of the second pole tip, so that the first pole piece and the second pole tip have the same track width at the ABS. This minimizes fringing of magnetic fields from the second pole tip laterally beyond the track width (side writing) to a wide expanse of the first pole piece.
A prior art process for notching the first pole piece entails ion beam milling the gap layer and the first pole piece, employing the second pole tip as a mask. According to this prior art process (typified in U.S. Pat. No. 5,452,164 and U.S. Pat. No. 5,438,747), the gap layer is typically alumina, and the first and second pole pieces and pole tips are typically Permalloy (NiFe). Alumina mills more slowly than Permalloy; thus the top of second pole tip and a top surface of the first pole piece are milled more quickly than the gap layer. Further, during ion milling, there is significant redeposition of alumina on surfaces of the workpiece. The milling ion beam is typically directed at an angle with respect to a normal to the layers, in order that milling and clean-up be done simultaneously.
Notching the first pole piece is very time consuming due, in part, to shadowing of the notch sites by the angled milling and by the profile of the second pole tip, as the wafer supporting the magnetic head is rotated, The length of milling time is due more, however, to the large lateral expanse of the first pole piece, Since the top and side walls of the second pole tip are also milled while the first pole piece is being notched, the second pole tip has to be formed with extra thickness and width so that, after notching is completed, the second pole tip is at its target height and target track width. Unfortunately, because of the long time required for notching it is difficult to meet the targets within acceptable tolerances. This has lowered manufacturing yield. Also, the extra height of the initially formed second pole tip increases the aspect ratio and reduces the line width of the second pole tip.
In order to minimize overmilling of the first pole piece, another process removes the gap layer, except for a desired portion between the first and second pole tips, by a wet etchant. After the unwanted portions of the gap layer are removed, the first pole piece is ion milled, employing the second pole tip as a mask. This process eliminates significant redeposition of the alumina. A problem with this process. however, is that the etching undercuts the gap layer under the base of the second pole tip, which is a critical area for the transfer of field signals. The undercut regions provide spaces where Permalloy can be redeposited during subsequent ion milling of the first pole piece, or other foreign material can be redeposited upon subsequent milling and clean-up steps. Further, if the track width of the second pole tip is in the order of 1 xcexcm. the etchant may release the second pole tip from the gap layer, thus ruining the head.
We have discovered that construction of a notching layer on a typical first pole piece layer with first and second corners adjacent the first and second side walls of the second pole tip will reduce the milling time required for notching. We construct the first pole piece layer with a wide lateral expanse, and the notching layer on the first pole piece layer with a narrow lateral expanse. We prefer the width of the notching layer to be 0.5 xcexcm to 2.0 xcexcm wider than the target track width of the second pole tip. With this arrangement, the notching layer has first and second side walls which project 0.25 to 1.0 xcexcm laterally beyond the first and second side walls, respectively, of the second pole tip. The thickness of the notching layer is, preferably, between 0.2 xcexcm to 1.0 xcexcm. Accordingly, full notching of the notching layer can be achieved by milling a small corner in a range of 0.25 xcexcm by 0.2 xcexcm to 1.0 xcexcm by 1.0 xcexcm, as seen in an ABS view. The gap layer is formed on the notching layer, followed by formation of the second pole tip on the gap layer. Milling at an angle is then employed to penetrate the gap layer and notch the notching layer. In comparison to the prior art where a large lateral expanse of the first pole piece is milled to achieve notching, milling the small corner of the notching layer requires a very short milling time. This results in less consumption of the second pole tip, so that better control of a final track width can be accomplished. Also, since there is less consumption of the top of the second pole tip, the aspect ratio of the photoresist employed to construct the second pole tip is lessened so as to enhance the line width of the second pole tip. Further, there is less redeposited material to clean up after the milling cycle. All of these factors reduce the process time and increase manufacturing throughput.
Another advantage of the present invention is that the milling that removes a second pole tip seed layer can be continued to perform notching. This still further lessens the process time by obviating any necessity of making a separate set up. Still another advantage is that the first pole piece layer and the notching layer of the first pole piece can be constructed of different materials, with different magnetic moments. Still a further advantage of the present invention is that the first pole piece can be notched on only one side, which provides the same benefits for servoing that are afforded by a double-notched first pole piece. A single-notched first pole piece can be formed by employing the above method, with the exception that the notching layer is given a wide expanse on the side that is not to be notched. Since the corner on the opposite side is quickly milled, there is very little notching of the wide expanse. It should be noted that single-side notching will also result in less redeposition of milled material.
Process time can still further be reduced with the single-side notching embodiment by forming the second pole piece with an asymmetrical flare and a matching notching layer. The second pole piece flares out laterally in first and second directions, from a recessed end of the second pole tip, to a recessed yoke portion of the second pole piece. The commencement of the flare is referred to as the flare point. We have discovered that by keeping a normal flare point on the side of the wide expanse, where the notching layer is not to be notched, and a flare point recessed from the normal flare point, on the side of the narrow expanse where the notching layer is to be notched, there is less shadowing of the notch site during the milling cycle. The notching layer is configured similarly to the second pole piece, with an asymmetrical flare portion and a border extension from the second pole piece. With this arrangement the second pole piece and the notching layer are further back on the side where notching is to take place, lengthening the time that the angled milling beam strikes the notching site during rotation of the wafer supporting the partially completed magnetic head.
An object of the present invention is to provide a method of notching a first pole piece with less processing time.
Another object is to provide a method of notching a first pole piece with more control of the target track width of the second pole tip.
A further object is to provide a method of notching a first pole piece with less consumption of the second pole tip and less redeposition to cleanup after notching the first pole piece.
Still another object is to provide a method wherein single side notching can be performed.
Still a further object is to provide a first pole piece of a magnetic head with a notching layer which is only partially notched.
Yet another object is to provide a first pole piece of a magnetic head that has different materials with different magnetic moments.